Low oxygen refractory metal powder for powder metallurgy

ABSTRACT

A method of making sheet bar and other precursors of formed products to be made by extensive working. The method includes providing a powder metal, preferably under 100 PPM oxygen content of non-spherical particles, compacting the powder into a coherent precursor form of at least 100 pounds, whereby a precursor is provided enabling extended fabrication to a finished product form. The finished product is resistant to breakup in fabrication due to oxide inclusion effect and produces a low oxygen end product. The method can process multiple species of metals that include at least one higher melting metal and one lower melting metal to produce an alloy or micro-composite of the metals as worked, where one metal is preferably a refractory metal (Ta, Nb, W, Wo, Zr, Hf, V and Re). The process is controlled to cause powder of the higher melting metal to be extended into a fibrous form.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of patent applicationSer. No. 09/377,077, entitled Low Oxygen Refractory Metal Powder forPowder Metallurgy filed on Aug. 19, 1999, and also claims priority ofProvisional Application Serial No. 60/223,771, entitled Tantalum orTantalum Alloy Sputtering Targets filed on Aug. 8, 2000, and both ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to powders and products oftantalum, niobium, and their alloys having low oxygen contents, andprocesses for producing the same.

[0003] The present invention is also a response to the problem ofestablishing high purity tantalum wire with under 100 PPM of oxygenimpurity for use as an effective lead wire for sintered tantalum powdersolid electrolytic capacitors. The invention also involves other metalsand usage of such other metals and tantalum in applications other thanas lead wires.

[0004] Other applications of the present invention include theproduction of aerospace alloys similar to those fabricated by theprocesses disclosed by Robert W. Balliett et al in their patents U.S.Pat. Nos. 5,918,104 issued Jun. 29, 1999 and 5,940,675 issued Aug. 17,1999.

[0005] The present invention also relates to composite materials andmethods of manufacturing the same, the composites including A-Bcombinations where A is selected from the group consisting of refractorymetals (Nb, Ta, W, Mo, Zr, Hf, Re) and their alloys with each other andstill further materials and B is selected from lower melting metalsincluding Cu, Al, Ni, Mg and alloys thereof.

[0006] The present invention also relates to metal sheets bent intonon-planar forms to provide an integral cone, cup angle bent or othershape without welded or otherwise joined seams and more particularly tosuch non planar sheets mode of refractory metals—Ta, Nb, Ti, Mo, W, Zr,Hf, Re—and more particularly Ta, Nb, including alloys of all theforegoing with each other and/or with other alloying ingredients.

[0007] The present invention further relates to sputter depositioncoating (sputtering) applying such refractory metals. In sputtering adischarge is created and ions from the discharge bombard a target, oftenof such refractory metal, and atoms of the metal or even gross particlesare pushed off the surface (sputtered) and deposited on a separatesubstrate. The target may be an electrode participating in forming thedischarge and/or accelerating ions to the target surface or may bepassive (with other electrodes serving for the discharge/acceleration).Sputter deposition is used in many applications including building up ofsolid state microelectronic components and integrated circuits, solidstate detectors and detector arrays, light emitting diodes and arrays ofsuch.

[0008] The invention also relates to usage of such refractory metals(elements, alloys) as containers for high temperature operations, e.g.serving as crucibles or rack mounts or other supports for holdingmaterials to be heated at temperatures above 1,500° C., sometimes above2,000° C.

[0009] The invention also relates to other forms of such refractorymetals which are fabricated into parts that are exposed to hightemperature and other adverse service condition usage, such as a leadingedge of an airplane or missile wing, fin, nose fairing, propeller bladewall, etc. exposed to one or more of temperature, wind, chemicals,vibration and a variety of static and dynamic loads in service usage.

[0010] The present invention also relates to production of large sizedmetal parts (mill products and fabricated parts) produced by extrusionof pre-formed compacts of metal powder to overcome the batch sizelimitations of conventional powder metallurgy and more particularly toseveral applications areas or such extrusion processing.

SUMMARY OF THE INVENTION

[0011] The invention comprises new powders of tantalum, niobium oralloys of tantalum or niobium having an oxygen content of less thanabout 300 PPM, preferably below 200 PPM and more preferably below 100PPM. The invention also comprises a method for producing these powderswherein hydrides of tantalum, niobium or alloy powders are heated in thepresence of an oxygen-active metal, such as magnesium.

[0012] The present invention comprises mixing of refractory metalpowders (one or more of Nb, Ta, Ti, W, Mo, Zr, Hf, Re, preferably Nb oralloys thereof) and lower melting matrix powder (one or more of Cu, Al,Ni, Mg, preferably Cu or alloys thereof) in a mass proportion andselected size ranges and morphology (particularly as the refractorymetal) to allow for subsequent mechanical working to a final fibrous orribbon form.

[0013] The powder blend is consolidated and subject to thermomechanicalworking and can include HIPing, extrusion, hot rolling, swaging, forgingand cold work steps such as rolling or wire drawing with or withoutintermediate or end anneals. The matrix metal is made with low oxygencontent to prevent fracture or other breakdown in the course of suchworking. The oxygen lowering treatment of exposure to alkaline earth(Mg, Ca) and/or hydrogen or hydrogen source (methane, ammonia, hydrides)can be employed.

[0014] Preferably the composite combination is a Cu—Nb blendencapsulated in an extrusion can and the thermomechanical workingcomprises extrusion to effect at least a 5:1, preferably 8:1 extrusionratio reduction.

[0015] The invention also comprises formed powder metal products havingoxygen contents less than about 300 PPM, preferably below 200 PPM andmore preferably below 100 PPM, formed from tantalum, niobium, and theiralloys. Further discovered is a new process for producing formed powdermetal products of tantalum, niobium and their alloys, having very lowoxygen contents without resistance sintering.

[0016] The present invention utilizes a combination and variation of thetwo lines of very old prior art development outlined above, takentogether with the further realization that this is a way to achieve apowder of very fine size with low oxygen usable in millproducts/fabricated parts manufacture. Normally the achievement of finesize (and related high surface area) of powder is associated with highoxygen pick-up deleterious to subsequent processing and use.

[0017] The object of the invention is achieved as to each of the severalapplication areas (sputtering, crucibles, curved aerodynamically shapeddevices, and others) by provision of integrally formed refractory metalsof curved sheet forms closed on themselves without use of welds, laps,seams or fasteners in the zone of usage challenge and preferablyentirely free of such artifacts. Such shapes may be referred to as potsor seamless pots. They are provided as deep or shallow cups or dishforms, cones (coming to a point or truncated), cylinders or partcylinders or part spheres, corrugated sheets or planar or curved sheetswith arrays of curving or conical dimples. The refractory metals may beof elemental or alloy forms and may be free standing or laminated tobackup sheets of lower cost or otherwise functional metals (e.g. copperfor electrical or thermal conductivity, steel or nickel alloys forstructural support, etc.).

[0018] One embodiment of the present invention pertains to sputteringtargets of refractory metals, and in particular tantalum and tantalumalloys, and methods of their fabrication. These targets arecharacterized by low oxygen, high density, fine grain-size and extremelyhigh uniformity in all directions, providing heretofore unachievablesputtering performance. The tantalum or tantalum alloy powder isproduced according to the method disclosed herein. The powder may beconsolidated to a high density by various techniques. The powder may becanned in copper, molybdenum-coated steel or other materials to protectit from contamination as it is consolidated at high temperature. The canmay or may not be removed by pickling or machining. The consolidatedmaterial may be thermo-mechanically processed to a sputtering target asdisclosed herein or by another method. For economic reasons, it iscommon practice to bond tantalum sputtering targets to copper plates orother substrates. In the case of powder canned in copper and possiblyother materials like molybdenum, using the can which bonds to the targetduring consolidation as the backing plate may eliminate this bondingstep.

[0019] A further embodiment of the present invention is the process ofmaking wires via a powder metallurgy route using tantalum hydridepowders that are packed into a shell. The powders are loosely filledinto the shell and then dehydrided in situ while loosely contained inthe shell. The shell is then closed in and used as an extrusion billetto produce a rod which can be used directly or subjected to further sizereduction by forging, swaging and/or wire drawing or rolling steps toproduce a final wire or sheet mill product and/or formed into a finalfabricated part at that time or later. Both the extrusion step and laterforming step(s) are made more effective by the original steps ofprovision of loose hydride powders into a container that will become anextrusion billet, dehydriding in situ and immediately sealing up thebillet to prevent oxygen absorption and then extruding. After cooling,the extruded product, i.e. the resultant rod, the original can materialnow constituting a thin surface layer of the rod can be removed. Theterm “rod” as used herein includes all sizes of the rod and wire rangepractically achievable via extrusion as well as all cross-section forms.

[0020] It is a principal object of the present invention to provide amethod of achieving fine tantalum and/or niobium powder with low oxygen,preferably averaging under 150 micrometer (micron) size and below 300PPM of oxygen, preferably below 200 PPM and more preferably below 100PPM.

[0021] This is accomplished by providing a fine size of tantalum hydridepowder of minus 150 microns and mixing it with a small amount ofmagnesium or calcium, less than ½% of the hydride weight. A precursor ofthe alkaline earth metal such as a hydride thereof can also be employed.The mixture is heated in a ramping up heating schedule to vaporize thealkaline earth metal and to start reduction of oxygen by the vapor,holding to complete the reaction of oxygen, then cooling, and acid andwater washing to leach off residual alkaline earth metal and drying toyield a tantalum powder of low oxygen (typically under 150 PPM) andparticle size averaging under 150 microns FAPD (Fisher Average particleDiameter).

[0022] An advantage of the powder of the present invention is that itcomprises relatively non-spherical particles suited for unidirectionalmechanical pressing.

[0023] A further advantage of the powder of the present invention isthat it comprises relatively small particles well suited for coldisostatic pressing.

[0024] An advantage of the formed products of tantalum, niobium or theiralloys, of the present invention, is that the products can be of anyshape, cross-section or size.

[0025] An advantage of the process for producing formed products of thepresent invention is that the process allows for the production oftantalum, niobium, or alloy formed products having low oxygen content asdescribed above and being of any shape cross-section or size.

[0026] In addition to application for Ta, Nb and alloys (Ta—Nb), theinvention can also be applied to other refractory metals, e.g., Mo, W,Ti, Zr, Hf, Re and alloys of the same with each other and/or Nb or Ta.

[0027] Other objects, features and advantages will be apparent from thefollowing detailed description of preferred embodiments taken inconjunction with the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWING

[0028]FIG. 1a is a flow chart showing a process of the present inventionto create low oxygen powder;

[0029]FIG. 1b-1 e are flow charts showing examples of forming steps tocreate products made of low oxygen powder;

[0030] FIGS. 2-4 are cross section views of seamless pots producedaccording to practice of the invention in a first preferred embodimentthereof utilizing forming techniques such as spinning;

[0031] FIGS. 5-7 are cross section views of seamless pots producedaccording to practice of the invention in a second preferred embodimentthereof using powder metallurgy (PM) to enable establishment of flangesor like extensions of the pots;

[0032]FIG. 8 is a flow chart showing practice of the invention accordingto a preferred embodiment thereof with a combination of PM and forming;

[0033] FIGS. 9-10 are sketches illustrating an emplaced seamless potsputtering target in a magnetron sputtering apparatus;

[0034] FIGS. 11-11A illustrate one of the forming processes describedherein;

[0035]FIG. 12 shows a typical I/M sputtering target after sputtering;

[0036]FIG. 13 shows a P/M sputtering target of the present inventionafter sputtering;

[0037]FIG. 14 is a schematic side view and FIG. 15 a front-end view ofan extrusion can (viewed as indicated by arrows A-A in FIG. 14) used inimplementing a preferred embodiment of the invention;

[0038]FIG. 16 is a flow chart of the above described process steps, asapplied to the case of making tantalum wire; and

[0039]FIG. 17 is a block diagram of the A-B process steps.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0040] The metal powders of low oxygen content of the present inventionare produced via the following procedure.

[0041] As illustrated in FIG. 1a, a first metal (including refractorymetals such as tantalum, niobium or alloy) hydride powder is placed intoa vacuum chamber, which also contains a metal having a higher affinityfor oxygen than the first metal, such as calcium or magnesium,preferably the latter. Preferably, the starting hydride powder hasoxygen content less than about 1000 PPM. The chamber is then heated tothe deoxidation temperature to produce a powder of tantalum, niobium oralloy of tantalum or niobium having a target reduced oxygen content ofless than about 300 PPM preferably below 200 PPM and more preferablybelow 100 PPM. The magnesium, containing the oxygen, is then removedfrom the metal powder by evaporation and subsequently by selectivechemical leaching or dissolution of the powder.

[0042] The following description and accompanying drawings relateprimarily to a specific embodiment, such as refractory metals, of theinvention, and the invention in its broader aspect should not be solimited to one specific embodiment as herein shown and described, butdepartures may be made therefrom within the scope of the accompanyingclaims without departing from the principals of the invention andwithout sacrificing its chief advantages.

[0043] The alloys of tantalum or niobium of the present inventioninclude alloys of tantalum and/or niobium, either or both with othermetals, and further includes incorporation of an oxide, which has ahigher free energy of formation than Ta and/or Nb oxide, such as forexample yttrium oxide, thorium oxide, or aluminum oxide. The oxide isblended into the tantalum and/or niobium powder having oxygen content ofless than about 300 PPM. The alloys of the present invention alsoinclude alloys of tantalum and/or niobium and a further alloying elementwith a low oxygen content blended into the tantalum or niobium powder,provided that the oxygen content of the blend is less than about 300PPM. The alloys of the present invention further include alloys oftantalum and/or niobium hydride and a further alloying element whereinthe alloying element and the tantalum and/or niobium hydride powder areblended prior to deoxidation to form the alloy having the low oxygencontent. The alloys of the present invention still further includealloys of tantalum and/or niobium and a further alloying element whereinthe oxygen addition associated with the alloying element does not raisethe oxygen content of the alloy above 300 PPM.

[0044] As described above, in the process for producing formed powdermetal products of tantalum, niobium and their alloys, the metal hydridepowder is deoxidized to an oxygen content of less than about 300 PPM.The powder is consolidated to form a tantalum, niobium or alloy product,having an oxygen content below about 300 PPM or 200 PPM or below 100PPM, but for many powder metallurgy purposes between about 100 PPM and150 PPM.

[0045] According to the present invention, a formed tantalum niobium oralloy product, having the low oxygen content, may be produced from metalhydride powder by any known powder metallurgy techniques. Exemplary ofthese powder metallurgy techniques used for forming the products are thefollowing, in which the steps are listed in order of performance. Any ofthe following single techniques or sequences of techniques may beutilized in the present invention:

[0046] cold isostatic pressing, sintering, encapsulating, hot isostaticpressing and thermomechanical processing;

[0047] cold isostatic pressing, sintering, hot isostatic pressing andthermomechanical processing;

[0048] cold isostatic pressing, encapsulating, hot isostatic pressingand thermomechanical processing;

[0049] cold isostatic pressing, encapsulating and hot isostaticpressing;

[0050] encapsulating and hot isostatic pressing;

[0051] cold isostatic pressing, sintering, encapsulating, extruding andthermomechanical processing;

[0052] cold isostatic pressing, sintering, extruding, andthermomechanical processing;

[0053] cold isostatic pressing, sintering, and extruding;

[0054] cold isostatic pressing, encapsulating, extruding andthermomechanical processing;

[0055] cold isostatic pressing, encapsulating and extruding;

[0056] encapsulating and extruding;

[0057] mechanical pressing, sintering and extruding;

[0058] cold isostatic pressing, sintering, encapsulating, forging andthermomechanical processing;

[0059] cold isostatic pressing, encapsulating, forging andthermomechanical processing;

[0060] cold isostatic pressing, encapsulating and forging;

[0061] cold isostatic pressing, sintering, and forging;

[0062] cold isostatic pressing, sintering and rolling;

[0063] encapsulating and forging;

[0064] encapsulating and rolling.

[0065] cold isostatic pressing, sintering and thermomechanicalprocessing;

[0066] spray depositing;

[0067] mechanical pressing and sintering;

[0068] mechanical pressing, sintering, repressing and resintering;

[0069] plasma assisted hot pressing;

[0070] plasma assisted hot pressing and extruding;

[0071] plasma assisted hot pressing and thermomechanical processing;

[0072] plasma assisted hot pressing, extruding and thermomechanicalprocessing.

[0073] Other combinations of consolidating, heating and deforming mayalso be utilized.

[0074] The effectiveness and advantages of the products and processes ofthe present invention will be further illustrated by the followingnon-limiting examples.

EXAMPLE 1

[0075] This example illustrates production of a tantalum powder withless than 300 PPM oxygen by deoxidation of tantalum hydride under apartial pressure of argon. Tantalum hydride powder, made by aconventional method as described above, was blended with 0.3 wt.-% Mgpowder and placed in a vacuum furnace retort, which was evacuated, andbackfilled with argon. The pressure in the furnace was set at 100microns with argon flowing and the vacuum pump running. The furnacetemperature was ramped to 650° C. in 50° C. increments, held untiltemperature equalized, then ramped up to 950° C. in 50° C. increments.When the temperature equalized at 950° C. it was held for two hours.After two hours at 950° C. the furnace was shut down and cooled to roomtemperature. Once the furnace cooled its powder content was removed fromthe retort. The magnesium, containing the oxygen, was then removed fromthe metal powder by acid leaching.

[0076] Properties of the resultant Ta powder were as follows: ParticleSize: −100 mesh (less than 150 microns) Oxygen: 240 PPM Surface Area:462 cm²/gm Specific Oxygen: 0.52 microgram/cm²

EXAMPLE 2

[0077] This example illustrates reduction of a tantalum powder with lessthan 200 PPM oxygen by the deoxidation of tantalum hydride under apartial pressure of argon. Tantalum hydride powder, made by conventionalmethod, was blended with 0.3 wt.-% Mg and placed in a vacuum furnaceretort, which was evacuated, and backfilled with argon. The pressure inthe furnace was set at 100 microns with argon flowing and the vacuumpump running. The furnace temperature was ramped to 850° C. in 50° C.increments, held until temperature equalized, then held for 3 hours. Itwas then ramped up to 950° C. in 50° C. increments. When the temperatureequalized at 950 ° C. it was held for two hours. After two hours at 950°C. the furnace was shut down and cooled to room temperature. Once thefurnace cooled its powder content was removed from the retort. Themagnesium, containing the oxygen, was then removed from the metal powderby acid leaching.

[0078] Properties of the resultant tantalum powder were as follows:Particle Size: −100 Mesh (less than 150 micrometers) Oxygen: 199 PPMSurface Area: 465 cm2/gram Specific Oxygen: 0.43 microgram/cm²

EXAMPLE 3

[0079] Tantalum powder with less than 100 PPM oxygen was produced by thedeoxidation of tantalum hydride under a positive pressure of argon.Tantalum hydride powder, made by conventional method, was blended with0.3 wt.-% Mg and placed in a production vacuum furnace retort, which wasevacuated, and backfilled with Argon. The pressure in the furnace wasset at 860 Torr with argon flowing. The furnace temperature was rampedto 650° C. in 50° C. increments, held until temperature equalized, thenheld for 4 hours. It was then ramped up to 1000° C. in 50° C.increments. When the temperature equalized at 1000° C. it was held forsix hours. After six hours at 1000° C. the furnace was shut down andcooled to room temperature. Once the furnace cooled its powder contentwas removed from the retort. The magnesium, containing the oxygen, wasthen removed from the metal powder by acid leaching.

[0080] Properties of the resultant Ta powder were as follows: ParticleSize: −100 Mesh (less than 150 microns) Oxygen: 77 PPM Surface Area: 255cm2/gm Specific Oxygen: 0.30 microgram/cm²

EXAMPLE 4

[0081] The following tests were conducted to show that the tantalum,niobium or alloy powder, of the present invention, is compressible, andto show the strength of the powder of the present invention. Tantalumpowder having an oxygen content of less than 300 PPM, prepared by aprocedure similar to the procedure of Example 1, was utilized as thestarting powder. The starting powder was placed in a die and pressed atvarious pressures, into tablets. The density of the tablets as afunction of the pressing pressures were as follows: Pressure Density(lbs./sq. in.) (% of Theoretical) 40,000 82 60,000 88 80,000 92 90,00093

[0082] These results show that the powders of the present invention arecompressible.

[0083] To show the strength of the powder of the present invention aftermechanical pressing tantalum powder having an oxygen content of lessthan 300 PPM, prepared by a procedure similar to the procedure ofExample 1, was placed in a die and pressed, at various pressures, intobars about ½ inch by about ½ inch, by about 2 inches. The transverserupture strength of these bars was as follows: Pressure TransverseRupture Strength (lbs./sq. in.) (lbs./sq. in.) 40,000 2680 60,000 538580,000 6400 90,000 8360

[0084] Generally a minimum strength of about 2000 lbs./sq. in. isdesired for normal handling of pressed compacts. The data from thecompressibility test together with the rupture strength test indicatesthat this strength level can be obtained with the powder of the presentinvention formed at a pressure of about 40,000 PSI.

[0085] Other Embodiments

[0086] In addition to the embodiments indicated above, the followingfurther embodiments can be made.

[0087] The production of a formed tantalum product having an oxygencontent of less than 300 PPM can be achieved by cold isostatic pressingof various kinds of known Ta/Nb powders to form a compact, followed by ahot isostatic pressing (HIP) step to densify the compact and thenthermomechanical processing of the powder compact for furtherdensification and completion of the bonding, as illustrated in FIG. 1b.Preferably, tantalum powder having an oxygen content of less than 300PPM, prepared by a procedure similar to the procedure of Example 1,would be utilized as the starting powder. This powder would be coldisostatically pressed at 60,000 pounds/sq. in. and room temperature,into a compact with rectangular cross-section, then hermeticallyencapsulated and hot isostatically pressed (HIPed) at 40,000 lbs./sq.in. and 1300 degrees C. for 4 hours. The HIPed compact would beunencapsulated and converted to sheet or foil by thermomechanicalprocessing steps.

[0088] A similar process, as illustrated in FIG. 1c, of just coldisostatic pressing, sintering and thermomechanical processing usingtantalum powder having an oxygen content of less than 300 PPM, preparedby a procedure similar to the procedure of Example 1, can be conductedby cold isostatically pressing at 60,000 lbs/sq. in. into a bar shapepreform. This preform would be sintered at 1500 degrees C. for 2 hoursin a vacuum of less than about 0.001 Torr to yield a preform having adensity of about 95% theoretical density (Th) and less 300 PPM oxygen.The sintered preform would be converted into sheet and foil bythermomechanical processing steps.

[0089] Formed tantalum bar and wire having an oxygen content of lessthan 300 PPM can be made by hot extrusion and thermomechanicalprocessing using tantalum powder having an oxygen content of less than300 PPM, prepared by a procedure similar to that of Example 1, as thestarting powder, and illustrated in FIG. 1d. This powder would behermetically encapsulated and then extruded through a circular die at1000° C. The extruded product would have oxygen content of less than 300PPM. The extruded preform was converted into rod and wire by thethermomechanical processing steps.

[0090] Another such process sequence, illustrated in FIG. 1e, is coldisostatic pressing, hot extrusion and thermomechanical processingutilizing tantalum powder having an oxygen content of less than 300 PPM,prepared by a procedure similar to that of Example 1, as the startingpowder. This powder would be cold isostatically pressed, hermeticallyencapsulated then extruded at 1000 ° C. The extruded product would haveoxygen content of about 300 PPM. It would be converted into rod and wireby the thermomechanical processing steps.

[0091] Production of a formed tantalum sheet or foil having an oxygencontent of less than 300 PPM by hot extrusion and thermomechanicalprocessing can be made, using tantalum powder having an oxygen contentof less than 300 PPM, prepared by a procedure similar to the procedureof Example 1, as the starting powder. This powder can be hermeticallyencapsulated then extruded through a rectangular die at 1000° C. toproduce an extruded product having oxygen content of less than 300 PPM.The extruded product can be converted sheet or foil by thethermomechanical processing.

[0092] Tantalum sheet or foil with oxygen content of less than 300 PPMcan be produced using the Example 1 powder by cold isostatic pressing,hot extrusion and thermomechanical processing. This compact made by coldisostatically pressing could be hermetically encapsulated then extrudedat 1000° C. to produce an extruded product with an oxygen content ofabout 300 PPM which can be converted into sheet and foil bythermomechanical processing steps.

[0093] A formed product of tantalum, produced by mechanical pressing andsintering. Tantalum powder having an oxygen content of less than 300PPM, prepared by a procedure similar to the procedure of Example 1,would be utilized as the starting powder. This tantalum powder wasplaced in a die and pressed, using uniaxial pressure, into a tablet witha pressed density of about 80% of the theoretical density. This tabletwas then sintered at 1500° C. for 2 hours in a vacuum evacuated to lessthan about 0.001 Torr. The final sintered tablet has oxygen content ofless than 300 PPM.

[0094] Tantalum products having oxygen content of less than 300 PPM canbe prepared by mechanical pressing, sintering, repressing andresintering. Tantalum powder having an oxygen content of less than 300PPM, prepared by a procedure similar to the procedure of Example 1, canbe utilized as the starting powder. It is placed in a die andmechanically pressed, using uniaxial pressure. The pressed tablet shouldbe then sintered at 1500° C. for 2 hours in a vacuum evacuated to lessthan about 0.001 Torr. The sintered tablet would then be repressed andresintered at 1500 degree C. for 2 hours in a vacuum evacuated to lessthan about 0.001 Torr. The resintered tablet will have oxygen content ofless than 300 PPM and be suitable for thermomechanical processing toproduce a formed tantalum product

[0095] Tantalum product having oxygen content of less than 300 PPM canbe prepared by spray deposition, using starting powder having an oxygencontent of less than 300 PPM, prepared by a procedure similar to theprocedure of Example 1. The powder can be spray deposited up to athickness of 0.1 inch on an alloy substrate formed from stainless steel.Particle size, flow properties and oxygen content of the powder will besuitable for consolidation by spray deposition.

[0096] Plasma activated sintering can be used for production of a formedtantalum product having oxygen content of less than 300 PPM. Tantalumpowder having an oxygen content of less than 300 PPM, prepared by aprocedure similar to the procedure of Example 1, would be utilized asthe starting powder. It would be poured into a tantalum foil linedgraphite die and graphite punches inserted into the die from both ends.The die punch assembly is placed on a water-cooled steel block. Anotherwater-cooled steel block is brought in contact with the top punch. Thewater-cooled steel block is attached to a hydraulic piston on the topand the base on the bottom to dissipate the heat accumulated during theconsolidation. The top and bottom water-cooled steel blocks are alsoattached to the positive and the negative ends of a DC power supply.

[0097] The powder filled die punch assembly is provided in a chamber.The chamber should be evacuated to 500 milliTorr. The consolidationwould be carried out in two stages. In the first stage, the intent isprimarily to purify the powder via plasma sputtering of particlesurfaces. A pressure of about 4300-psi would be applied on the powderthrough the punches and a pulsed DC current of 1000 A would be passedthrough the powder. These conditions would be maintained for twominutes.

[0098] During the second stage the pressure would be raised to about6500 psi and non-pulsed DC current of 4500 A passed through the powder.These conditions would be maintained for two minutes. At the end of thecycle, the power to the punches is turned off, the vacuum pump is turnedoff and the evacuation chamber backfilled with nitrogen. The die punchassembly is allowed to cool to the room temperature and the consolidatedtantalum sample is removed from the die. The consolidation cycle wouldbe about eight minutes. The sintered preform will have a density of over95% of the theoretical density and oxygen content of less than 300 PPM.

[0099] A niobium powder with less than 300 PPM oxygen can be produced bythe deoxidation of niobium hydride under partial pressure of argon.Niobium hydride powder would be blended with 0.3 wt.-% Mg and placed ina vacuum furnace retort, which is evacuated, and backfilled with argon.The pressure in the furnace would be set at 100 microns with Argonflowing and the vacuum pump running. The furnace temperature would beramped to 650° C. in 50° C. increments, held until temperatureequalized, then ramped up to 950° C. in 50° C. increments. When thetemperature equalized at 950° C. it would be held for two hours. Aftertwo hours at 950° C. the furnace is shut down. Once the furnace coolsits powder content is removed from the retort. The magnesium, containingthe oxygen, would then be removed from the metal powder by acid leachingto produce the resulting niobium powder having an oxygen content of lessthan 300 PPM.

[0100] A seamless pot is made by providing a plate form (e.g. rectangleor round disc or other form) of a refractory metal and spinning to thedesired pot form. Spinning ‘bends’ a plate into a cup by pressing on oneside of the metal. Flow forming elongates the wall of the cup bysqueezing it between an interior form and an exterior wheel. Theoriginal planar form can be provided by arc or electron beam or plasmamelting or powder metallurgy, and cold or hot reduction to sheet form byextrusion, forging and/or rolling. The spinning process and equipmentare per se well known and as a practical matter dependent on asufficiently thin section of the planar refractory metal for effectiveconduction. In turn thinner sections of the refractory metal are enabledunder the present invention because in service use the metal won't beexposed to selective erosion (e.g., as in the preferential sputtering ofweld joints). Sample forms of the spun metal sheet are shown as finishedpots in FIGS. 2-4.

[0101] Under a second embodiment of the invention powder of therefractory metal is cold pressed to the thin section pot shape and thenconsolidated by sintering or hot isostatic pressing (HIPing). This canalso incorporate an extra element of a very sharp bend such as a flangearound the pot edge that would be unduly difficult to establish for therefractory metal by spinning. Sample forms of the finished pots withflanges as producible by cold pressing and HIPing are shown in FIGS.5-7.

[0102] A third embodiment is illustrated by the flow chart of FIG. 8.Sheets are formed by the powder metallurgy (PM) method described aboveand HIPed but with a deliberate thicker section than desired for end useas a whole or in parts. The sheet is then subjected to a flow formingprocess of local rolling, swaging, upset forging or the like to thin itout and eliminate nonuniformities of thickness and in the course ofdoing so completing consolidation of the curved part, which can have anyof the shapes of FIGS. 2-7 or other nonplanar forms.

[0103] A still further embodiment of the invention is the production ofpots from a billet of the refractory metal by back extrusion.

[0104] Some details of implementation follow:

[0105] To implement the PM approach, a refractory metal or alloy powderof −100 mesh may be cold pressed into near-net shape of a sputter targetat 60 KSI. It may be encapsulated in a steel can and hermetically sealedin vacuum. The sealed assembly may be hot isostatically pressed at 500KSI/1200° C. for four hours. The steel may be removed by pickling inacid. The near-net shape may be machined into a ready-to-use component.

[0106] In one application, the machined part may be used in a hollowcathode magnetron sputtering apparatus as shown in FIG. 9; itsperformance will be superior to that of a welded target as measured bythe uniformity of the deposited film and the formation of nodules on thesurface of the target.

[0107] A refractory or alloy powder of −100 mesh may be cold pressedinto a disk of 6.5″ diameter and 2″ height at 60 KSI. It may beencapsulated in a steel can and hermetically sealed in vacuum. Thesealed assembly may be hot isostatically pressed at 50 KSI/1200° C. forfour hours. The steel can be removed by pickling in acid. The disk maybe converted into a pot by one of (a) back extrusion, (b) spin forming,(c) flow forming, or (d) a combination of such processes. The pot may beannealed at 1300° C. for 90 minutes in a vacuum environment.

[0108] A refractory metal or alloy powder of −100 mesh and having asuitable chemistry, including metallic and interstitial impurities, maybe cold pressed into a disk of 6.5″ diameter and 2″ height at 60 KSI. Itmay be sintered at 1500° C. for four hours in a vacuum environment. Thedisk may be converted into a pot, as in (2) above and annealed and used.

[0109] Tantalum powder of −100 mesh and having a suitable chemistry forsputter target usage, including metallic and interstitial impurities,was encapsulated in a 7″ diameter copper can and hermetically sealed invacuum. It was extruded at 1050° C. through a 2″×1″ rectangular die. Thecan was removed by pickling. The extruded bar was annealed at 1370° C.and processed into 0.2″ thick plate by rolling. The rolled plate wasannealed at 1370° C. The performance of the annealed plate was utilizedand characterized in magnetron sputtering with acceptable results.

[0110] (5) A tantalum metal ingot, having a suitable chemistry forsputtering target usage, including metallic and interstitial impurities,was forget to the shape of a sheet-bar and annealed at 1370° C. It wasrolled to 0.55″ thickness, annealed, and cut to the shape of a disc. Thedisc was spun to the shape of a cup, 5″ high and 10″ diameter, which wasannealed again. The cup was flow-formed to thin the sidewalls andincrease the height to 10″, then annealed again, at 1065° C. The finalgrain size, at the top of the sidewalls, was ASTM 5 to ASTM 6.

[0111] (6) A refractory or alloy powder of −100 mesh may be encapsulatedin a copper can 7″ diameter or larger and hermetically sealed in vacuum.It may be extruded at 1050° C. through a rectangular die 5″×2″. The canmay be removed by pickling. The extruded bar may be annealed at 1370° C.and processed into 0.55″ thick plate by rolling, annealed again, and cutto the shape of a disc. The disc may be spun to the shape of a cup, 5″high and 10″ diameter, which will be annealed again. The cup may beflow-formed to thin the side-walls and increase the height to 1−″, thenannealed again at 1065° C.

[0112] FIGS. 9-10 show (in part) a magnetron sputtering apparatus 100with a cathode assembly 102 as a water cooled block with a largereservoir as shown or bonded on coolant pipes having an curved cathodeface portion 104 made of an assembly of a seamless refractory metal pot104A, made as described above in various embodiments, and a backingplate 104B of steel, copper, aluminum or other metal secured to therefractory metal pot by epoxy or weld bonding and/or back coating. Atypical sputter environment is a back fill of argon at 10-2 mm Hgpressure. A substrate is indicated at S (and there can be many suchsubstrates on fixed or movable jigs). The plasma established standardmeans (not shown).

[0113] FIGS. 11-11A illustrate flow-forming wherein a cup 110 made,e.g., by PM to near-net shape say, 0.5″ thickness can be flow-formed byforming sheets W1, W2, W3 to a lesser thickness while the cup is mountedon a mandrel on a clamped by a clamp block C, the whole assemblyrotating. As the thickness is reduced the wheels are displaced axiallyalong the cup. As thickness of the up wall is reduced its lengthincreases correspondingly.

[0114] It will be understood that the nonplanar sputter targets of thepresent invention through their freedom from weld joints and controlleduniformity can afford longer life and avoidance of expensiveover-design, yet provide significant assurance against breakthroughs ofcoolant or exposure of backing plate to the sputter environment.

[0115] The improved sputtering target of the present invention isproduced using a tantalum powder containing less than 150 PPM oxygen andless than 100 PPM of metallic impurities. Powders made from tantalumalloys (including but not limited to the alloys TaNb, TaMo, TaW, TaSi,TaAl) may also be used. The powders are pressed into a disk and the diskencapsulated in a metallic container such as copper or steel.Consolidation of the tantalum powder may be done by sintering,resistance sintering, hot isostatic pressing (HIPing), extrusion orother techniques. In all cases, it may be beneficial to apply subsequentthermo-mechanical processing (TMP) after consolidation, since theprocessing will close some porosity and/or might improve grain size ortexture. Deformation steps may include forging, orbital forging orrolling.

[0116] In one embodiment, a copper container is evacuated, filled withtantalum powder, hermetically sealed, and extruded through a die to givea 10:1 extrusion ratio. The copper container is removed by acidtreatment and the extruded bar is thermo-mechanically processed into asheet form flat or curved tantalum sputtering target. In anotherembodiment, a steel container is evacuated, filled with the tantalumpowder, hermetically sealed and HIPed. The steel container is removed bymachining and the HIPed piece is thermo-mechanically processed into asheet form flat or curved tantalum sputtering target.

[0117] Anneals may be used to improve workability of the material inbetween two deformation steps or to adjust grain size and texturethrough recrystallization although a final anneal may not be necessary.When the powder is canned during the consolidation (usually to protectit from the environment at high temperature), the can will bond to thetantalum. In manufacturing the sputtering target, the bonded sheath ofthe formed composite billet may be used as backing plate and therebyeliminate the bonding procedure.

[0118] The P/M target of the present invention inherently yields asuperior uniformity of properties, including grain size and texture, ascompared to the I/M target and therefore yields a better uniformity ofthe sputtered film. Using the can material as a backing plate for thetarget eliminates one processing step in the manufacture of sputteringtargets and contributes to a more economical process.

[0119] Referring to FIGS. 12 and 13, 5″×8″ sputtering targets were madeaccording to traditional I/M processes and according to the P/M processof the present invention, respectively. The I/M sputtering target 10consists of a thin sheet of tantalum 12, bonded to a backing plate 14.FIG. 12 illustrates how the I/M sputtering target 10 erodesnon-uniformly after sputtering. Non-uniform grain size and/or texturecause the line-like patterns 16 in the trench of the I/M target 10. TheP/M sputtering target 20 consists of a thin sheet of tantalum 22 bondedto a backing plate 14. FIG. 13 illustrates how the P/M sputtering target20 of the present invention erodes uniformly after sputtering. The matteappearance of the P/M target's surface is caused by uniform sputteringefficiency throughout the target.

[0120] In another embodiment, the process provides P/M sheets of largesize (>50 pounds) having good mechanical properties and small grainsize, capable of a higher yield than conventional P/M processes forsheet manufacture, typically 20 pounds. Low oxygen Ta or Nb powder ofless than 200 PPM, preferably less than 150 PPM, of non-sphericalparticles and sizing less than_microns (FAPD), is provided per processesdescribed herein. Powders with a higher content in oxygen cannot beconsolidated to full density and/or will not yield good mechanicalproperties. The powder is consolidated either by HIPing (hot isostaticpressing) or by extrusion. Preferably, the powder is compacted into acoherent precursor form of at least 100 pounds with a density of 80-90%theoretical. The precursor density is brought to 95-100% theoretical.Both methods of consolidation are capable of providing suitable P/Msheet bars with a weight of up to several hundred pounds.Thermomechancial processing of the P/M sheet bar is similar to standardprocesses.

Comparative Example I (a Two Step Process)

[0121] The following comparative examples illustrate the benefits of thepresent invention.

[0122] This example illustrates the prior art. Tantalum hydride powdermade by conventional methods was dehydrided at 650° C. for ten hoursthen cooled and removed from the retort. It was then blended with0.5-wt% Mg and placed in a vacuum furnace retort, which was evacuated,and backfilled with argon. The pressure in the furnace was set at 860Torr with argon flowing. The furnace temperature was tamped to 1000° C.When the temperature equalized at 1000° C. it was held for six hours.After six hours at 1000° C. the furnace was shut down and cooled to roomtemperature. Once the furnace cooled, its powder content was removedfrom the retort. The magnesium-containing oxygen was then removed fromthe metal powder by acid leaching. Properties of the resultant Ta powderwere as follows: Particle size: −100 mesh (less than 150 microns)Oxygen: 145 PPM Surface area: 250 cm²/gm Specific oxygen: 0.58microgram/cm²

[0123] A comparison of this example with Example 3 above illustratesthat the deoxidation of tantalum hydride results in significantly lowerlevels of oxygen in tantalum powder.

Comparative Example II

[0124] Tantalum hydride powder made by conventional methods wasdehydrided at 650° C. for ten hours then cooled and removed from theretort. It was then blended with 0.5 wt-% Mg (present invention) andplaced in a vacuum furnace retort, which was evacuated and backfilledwith argon. The pressure in the furnace was set at 100 microns withargon flowing and the vacuum pump running. The furnace temperature wasramped to 850° C. in 50° C. increments. When the temperature equalizedat 950° C. it was held for two hours. After two hours at 950° C. thefurnace was shut down and cooled to room temperature. Once the furnacecooled its powder content was removed from the retort. The magnesium,containing oxygen, was then removed from the metal powder by acidleaching.

[0125] Oxygen contents of deoxidized tantalum hydride (Example 2) andtantalum powder are given below for various size fractions obtained fromthe one step (present invention) and two step (Comparative II)processes. Oxygen on Deoxidized Tantalum Oxygen of Deoxidized Hydride(in PPM) Tantalum (in PPM) Particle size (one thermal cycle) (twothermal cycles) Minus 100 mesh 199 345 100/140  86 182 140/200 107 207200/270 146 270 270/35 147 328 Minus 325 367 615

[0126] Numerous variations and modifications may obviously be madewithout departing from the present invention. Accordingly, it should beclearly understood that the forms of the present invention hereindescribed are illustrative only and are not intended to limit the scopeof the invention.

[0127] As shown in FIGS. 14-15, an extrusion can 10 usable in theprocess of the invention comprises a ten to twenty inch long, 6.25 in.diameter 0.060 in. wall cylinder 12 copper or copper-nickel alloy, a 4-5inch long (approx.) conical front end 14, and an evacuation tube 16 of0.040 in. wall copper tubing of about six inches length. A solid copperblock 18 is welded into the tube's back end. These sizes are scalable upsubstantially to extrusion billets of several feet long and up to 10-20in. diameter.

[0128]FIG. 16 shows the process in block diagram form comprising thesteps of (I) provision of tantalum hydride powder of 44-250 mesh form or(preferably) minus 120 mesh; (II) forming an extrusion can as shown inFIGS. 1-2 and described above; (III) filing the can with the tantalumhydride powder; (IV) dehydriding the powder; (V) closing “the canopening”; (VI) extruding the filled can.

[0129] As mentioned above, loose dehydrided powders are inserted intothe interior 17 of the cylinder 12, filling via tube 16. Then the can 10as a whole is placed in a vacuum furnace to dehydride the powders, ineffect pumping via tube 16. The feed end is sealed off and the tube as awhole (billet) can then be extruded.

[0130] Hydriding of tantalum powders to embrittle them for use in powderproduction per se is well known in the capacitor powder arts. See, e.g.,U.S. Pat. No. 3,295,951 of Fincham and Villani. It is also well known toadd hydrogen to dispersion strengthened metals (e.g. copper, nickel,iron powders strengthened with aluminum oxide inclusions) to reduce anyresidual oxygen; this is exemplified by teachings of the following U.S.patents of SCM Corporation: U.S. Pat. No. 3,779,714 (Dec. 18, 1973),U.S. Pat. No. 3,884,676 (May 20, 1975), U.S. Pat. No. 3,893,844 (Jul.18, 1975), U.S. Pat. No. 4,440,572 (Apr. 3, 1984). Following my conceptof hydride usage, described above, it was disclosed and claimed by I.Friedman to make tantalum hydride powder, cold isostatic press (CIP) thepowder into a billet, dehydride the billet and extrude the billet afterwrapping it in a double jacket, with a powder separation between jacketlayers. See U.S. Pat. Nos. 5,445,787 (Aug. 29, 1995) and 5,482,672 (Jan.9, 1996).

[0131] All the above cited other approaches miss the fundamental pointof the present invention—combining a full hydriding of powders toproduce a hydrided preform, comminuting it to a desired size whileexcluding oxygen, dehydriding under a condition where adequateelimination of the hydrogen can be obtained without reintroducing oxygenat unacceptable levels (i.e. loose hydride powders in a shell),completion of the billet configuration and extrusion.

[0132] The assembled billet is reduced in size and the powders thereinare simultaneously consolidated to a coherent workable form in thecourse of extrusion.

[0133] An additional embodiment of the invention applies the process toNb—Cu composites. As illustrated in FIG. 17, Powder A (for example Nb)and B (for example Cu) are blended, canned, extruded, and rolled. Lowoxygen copper and niobium powders are used. The physical processes ofblending, canning and extruding achieve a uniform distribution ofniobium particles of a controlled size in the copper matrix. Onsubsequent rolling, a uniform distribution of niobium fibers isproduced. Low oxygen niobium powder is produced. Magnesium-Ca, or othermetals may also be used to achieve reduction of niobium hydride.Judicious heat treatment of copper powder in a hydrogen atmosphere givesless than 300 PPM oxygen without any significant agglomeration of thepowder. The low-oxygen blend of Cu—Nb (or Ta, Mo or W) can also beprocessed into the final products by other methods, normally used forthe manufacturing of powder metallurgy mill products, and powdermetallurgy parts, including, but not limited to, HIPing, pressing plussintering.

[0134] The blending, canning, extruding, and rolling of low oxygencopper and niobium powders can achieve a uniform distribution of niobiumparticles of a controlled size in the copper matrix. The low oxygenniobium powder (or other refractory metal powder) can be produced via amagnesium reduction process as described above.

[0135] Sieving of the powder is used to control the initial niobiumpowder size. Annealing the copper powder in a hydrogen atmosphere thencooling in inert gas produces low oxygen copper powder. A trace leveladdition of a material such as SiO₂ helps to prevent agglomeration ofthe copper powder. These powders are then blended under inert conditionsto produce the desired alloy composition. The powders are then sealed inan evacuated can, heated to a desired temperature, and extruded suchthat the extrusion ratio is at least 8:1. This is done to completelyconsolidate the copper and niobium powders. On subsequent rolling, auniform distribution of niobium fibers is produced. The can may beremoved either just before or just after the rolling operation. Thecanning and extrusion can be as described in detail above.

[0136] The above process can afford advantages of more uniform noduledistribution in the final material, more uniform material properties,lower manufacturing costs, better control of fiber size, and greaterflexibility for alloy modifications and control of properties.

[0137] Alternatively, the blended powders may be isostatically pressedinto a bar prior to canning and extrusion. The advantage of this methodwould be to put a higher weight into the compact prior to extrusion toaid in consolidation.

[0138] In another embodiment of the invention, blending, canning,extruding, and rolling of low oxygen copper and niobium powders canachieve a uniform distribution of niobium particles of a controlled sizein the copper matrix. On subsequent rolling, a uniform distribution ofniobium fibers is produced. Low oxygen niobium powder is produced bymagnesium (Ca, or other metals may also be used) reduction of niobiumhydride.

[0139] Judicious heat treatment of copper powder in a hydrogenatmosphere gives less than 300 PPM oxygen without any significantagglomeration of the powder. The low-oxygen blend of Cu—Nb (or Ta, Mo orW) can also be processed into the final products by other methods,normally used for the manufacturing of powder metallurgy mill products,and powder metallurgy parts, including, but not limited to, HIP′ing andpressing plus sintering.

[0140] Another use of the invention is to manufacture mill products andparts requiring unique properties (high strength, high electricalconductivity, high thermal conductivity, resistance to softening,resistance to arcing and other examples include annealing bands, weldingelectrode tips among others.

[0141] The hydriding can and the metal hydride are more easilycomminuted than the respective metal and this can be used to advantagein another embodiment. The hydride is compacted into the form of thindisks by cold isostatic pressing and the disks are deoxidized by heatingin an inert atmosphere (except for presence of a source of a source ofvapor of a reduction metal such as Mg or Ca), the combined effect ofdehydriding heating and metal vapor reduction lowering the oxygencontent of the disks to below a target level, typically under 100 PPM.Residual magnesium oxide is removed by acid leaching. The disks are thenstacked in a pre-formed copper extrusion can. In particular areas ofpractice of the invention, the disks described above can be made with acenter hole and as stacked have an elongated hole that is filled, beforeor after insertion into the extrusion billet, with a rod. The extrudedand further worked end product can be used for several purposes. Whenthe disks are Ta or Nb with a Ti rod core, then the resultant extrudedand worked (drawn to wire and Cu sheathing removed) can be used as acomposite lead wire for, e.g., Ta anodes, of capacitors, the wirecomprising a titanium core and Ta or Nb sheath well bonded to each otherwith a reduced cost basis because of the lower cost of titanium relativeto tantalum, but substantially as functional mechanically andelectronically as if wholly tantalum.

[0142] In a further embodiment the powder can be deoxidized/dehydridedand the low oxygen powder that is produced can be made into disks forstacking and extruding (with or without a rod core inserted).

[0143] It will now be apparent to those skilled in the art that otherembodiments, improvements, details, and uses can be made consistent withthe letter and spirit of the foregoing disclosure and within the scopeof this patent, which is limited only by the following claims, construedin accordance with the patent law, including the doctrine ofequivalents.

What is claimed is:
 1. A method of making sheet bar and other precursorsof formed products to be made by extensive working comprising: providinga metal as a powder under 250 PPM oxygen content of non-sphericalparticles, compacting the powder into a coherent precursor form of atleast 100 pounds, whereby a precursor is provided enabling extendedfabrication to a finished product form, which is resistant to breakup infabrication due to oxide inclusion effect and produces a low oxygen endproduct.
 2. The method of claim 1 wherein the powder has under 100 ppmoxygen.
 3. The method in accordance with either of claims 1 or 2 whereinthe metal is a refractory metal Ta, Nb, W, Wo, Zr, Hf, V and Re).
 4. Themethod of either of claims 1 or 2 wherein multiple species of metals areprovided.
 5. The method of claim 4 wherein the multiple species includeat least one higher melting metal and one lower melting metal to producean alloy or micro-composite of the metals as worked.
 6. The method ofclaim 5 wherein the process is controlled to cause powder of the highermelting metal to be extended into a fibrous form.
 7. The method of claim5 wherein the higher melting metal is a refractory metal.